1. Field of the Invention
This invention relates to a method for operating a mass flowmeter that employs the Coriolis principle and encompasses a measuring tube through which flows a medium and which is stimulated into oscillating at a minimum of one frequency, allowing the resulting oscillations to be detected and measured.
2. The Prior Art
Coriolis mass flowmeters operated by the method referred to above have been well known in the prior art, as described for instance in DE 100 02 635 A1. Conventional Coriolis mass flowmeters often employ natural self-resonance, i.e. they are energized at a self-resonant frequency—also referred to as the natural frequency—of the measuring tube. A change in the natural frequency of the measuring tube through which flows a medium relative to the natural frequency of an empty measuring tube provides an indication of the density of the flowing medium. Another variable of interest is the viscosity of the medium flowing through the measuring tube.
In conventional Coriolis mass flowmeters, one approach, described for instance in DE 100 20 606 A1, has been to generate torsional vibrations of the measuring tube and to measure the viscosity by determining the amount of increased energy consumption brought about by the shearing strain bearing on the medium. That method, however, is susceptible to certain deficiencies which considerably compromise accurate viscosity determinations.